Split airflow system for an electrically heated smoking system and method for guiding an airflow inside an electrically heated smoking systems

ABSTRACT

An assembly for an aerosol-generating system is provided, including: a liquid storage portion configured to hold a liquid aerosol-forming substrate; a mouthpiece having an outlet opening at a proximal end; and a heater assembly including an electrical heating element configured to heat the substrate to form an aerosol, and a porous capillary material disposed in contact with the heating element and including a ceramic or a ceramic-based material, the heating element being disposed along a surface of the capillary material, the liquid storage portion being disposed at a first side of the heater assembly and a first airflow channel is disposed at a second side of the heater assembly, the first airflow channel defining an airflow path that extends in a direction perpendicular to the surface of the capillary material and is directed at a center of the heating element. An aerosol-generating system and a heater assemble are also provided.

The invention relates to electrically heated smoking systems and amethod for guiding an airflow inside an airflow inside an electricallyheated smoking system.

Some aerosol-generating systems such as electrically operated smokingdevices may comprise a battery and control electronics, a cartridgecomprising a supply of aerosol forming substrate and an electricallyoperated vaporizer. A substance is vaporized from the aerosol formingsubstrate, for example by a heater. An airflow is made to pass theheating element to entrain the vaporized liquid and guide it through amouthpiece to a mouth end of the mouthpiece, while a user is puffing atthe mouth end.

The airflow passing the heater may have a cooling action on the heater.This may lead to less vaporized liquid or may require more energy tokeep the heater at a temperature sufficient for vaporizing an amount ofliquid such as to achieve a desired amount of aerosol.

Thus, there is a need for electrically heated smoking systems and for amethod for guiding an airflow inside electrically heated smoking system,which improve the efficiency of the electrically heated smoking system.

According to a first aspect, there is provided a split airflow systemfor an electrically heated smoking system for generating aerosol. Thesplit airflow system has a downstream end and comprises a first channeldefining a first flow route and a second channel defining a second flowroute. The first channel and the second channel are at least partiallydistinct channels. The first flow route directs ambient air from outsidethe system to the downstream end of the system. The second flow routedirects ambient air from outside the system towards a heating element,preferably a substantially flat, fluid permeable heating element, beforeconveying the ambient air to the downstream end. The first channel andthe second channel define a total volume of ambient air passing throughthe system and the first channel provides at least 50 percent of thetotal volume of ambient air passing through the system.

Liquid vaporized by the heating element is collected by ambient airflowing in the second channel and is transported to the downstream endof the split airflow system. Ambient air is guided into the splitairflow system and passes the heating element for taking up the liquidthat has been vaporized by the heating element. This ambient air coolsthe heating element. The cooling effect is not only dependent on thetemperature of the ambient air but also on the amount of ambient aircoming into contact with the heating element. A first channel fordirecting ambient air along a first flow route not passing the heatingelement is now provided in the split airflow system according to theinvention. The first channel also ends at the proximal end of thesystem, preferably at a mouth end of a mouthpiece of an electricallyoperated smoking system. However, ambient air entering the split airflowsystem is split along the first flow route and the second flow route inthe first channel and the second channel, respectively. Preferably, thefirst channel bypasses at least those portions of the second channelthat are arranged upstream of the position of the heating element. Bythis, only a portion of the total volume of ambient air entering thesystem passes the heating element. Another portion of the total volumeof ambient air is directly, that is without passing the heating element,guided to the downstream end of the split airflow system.

By this measure, a variable volume of ambient air may be bypassing theheating element. The ambient air that passes the heating element andthat may have a cooling effect on the heating element may be varied andmay be controlled. Since only half or preferably less than half of thetotal volume of ambient air passes the heating element, the heatingelement is not cooled as much as if the total volume of ambient airwould be passing the heating element. Thus, the heating element may beoperated at lower energy. This saves energy and may lead to a battery ofa smoking system comprising the split airflow system to have longeroperating hours or may lead to a downsizing of such a battery. Inaddition, if a heating element may be operated at lower energies, therisk of a malfunctioning of the heating element, for example due toelectrical short-cuts, or high temperature spikes, may be reduced oromitted.

Yet further, since the ambient air in the first channel has not passedthe heating element, this ambient air is cooler than the aerosolcarrying ambient air in the second channel. Thus, the ambient air in thefirst channel may have a cooling effect on the aerosol carrying ambientair. This effect is in particular pronounced, if the first flow route isjoined with the second flow route before reaching the downstream end ofthe system. Then the first airflow is mixed with the second airflowinside, for example, inside a mouthpiece and is cooled more rapidly.This may result in oversaturation of the air with the vaporized liquid.This again may result in the formation of smaller aerosol droplets.

Preferably, the first channel provides between about 50 percent andabout 95 percent of the total volume of ambient air passing through thesplit airflow system. More preferably, the first channel providesbetween about 65 percent and about 95 percent of the total volume ofambient air passing through the split airflow system, even morepreferably, between about 85 percent and about 89 percent.

It has been found that a small airflow passing the heating elementsuffices to entrain the vaporized liquid and guide it to a downstreamend of the system. The smaller the ambient airflow passing the heatingelement, the less heat loss due to cooling of the heating element by thepassing airflow. The above flow volumes of the second channel have shownto entrain vaporized liquid particularly well and by an at the same timelow cooling of the heating element.

Preferably, the mentioned percent of volume of the total volume ofambient air are applied in an aerosol generating smoking systempreferably comprising a substantially flat heating element, morepreferably a substantially flat, fluid permeable heating element, forexample a heating element comprising a plurality of electricallyconductive filaments such as a mesh heating element.

The volume of the ambient air passing through the second channel andpassing the heating element may be varied and adapted to, for example,the kind of heating element applied or the amount of vaporized liquidavailable. For example, the volume of ambient air passing the heatingelement may be adapted to a total area, which is effectively heated bythe heating element.

As a general rule, whenever the term ‘about’ is used in connection witha particular value throughout this application this is to be understoodsuch that the value following the term ‘about’ does not have to beexactly the particular value due to technical considerations. However,the term ‘about’ used in connection with a particular value is always tobe understood to include and also to explicitly disclose the particularvalue following the term ‘about’.

The terms ‘upstream’ and ‘downstream’ are used herein in view of thedirection of an airflow in the system. Upstream and downstream ends ofthe system are defined with respect to the airflow when a user draws onthe proximal or mouth end of the aerosol-generating smoking article. Airis drawn into the system at an upstream end, passes downstream throughthe system and exits the system at the proximal or downstream end. Theterms ‘proximal’ and ‘distal’ as used herein refer to the position of anelement with respect to its orientation to a consumer or away from aconsumer. Thus, a proximal end of a mouthpiece of aerosol-generatingsystem corresponds to the mouth end of the mouth piece. A distal openingof a cartridge housing corresponds to a position of an opening arrangedin the cartridge housing facing away from a consumer, accordingly.

The term ‘substantially flat’ heating element is used throughout thespecification to refer to a heating element that is in the form of asubstantially two dimensional topological manifold. Thus, thesubstantially flat heating element extends in two dimensions along asurface substantially more than in a third dimension. In particular, thedimensions of the substantially flat heating element in the twodimensions within the surface is at least 5 times larger than in thethird dimension, normal to the surface. An example of a substantiallyflat heating element is a structure between two substantially parallelimaginary surfaces, wherein the distance between these two imaginarysurfaces is substantially smaller than the extension within thesurfaces. In some preferred embodiments, the substantially flat heatingelement is planar. In other embodiments, the substantially flat heatingelement is curved along one or more dimensions, for example forming adome shape or bridge shape. A flat heating element can be easily handledduring manufacture and provides for a robust construction.

Heating elements as used in the split airflow system or in the smokingsystem may for example be wick-coil heaters as known on the art.Therein, a coil is wound around a wick, which wick is immersed into aliquid to be vaporized. The liquid is transported by capillary actionoutside of its cartridge to the portion of the wick where the coil iswound around the wick and heating this wick portion.

Preferably, fluid permeable heating elements are used. Fluid permeableheating elements are suitable for vaporizing liquids of different kindof cartridges. For example, as a liquid aerosol-forming substrate, acartridge may contain a liquid or a liquid containing transport materialsuch as for example a capillary material. Such a transport material andcapillary material actively conveys liquid and is preferably oriented inthe cartridge to convey liquid to the heating element. A filamentarrangement of the heating element is arranged close to the liquid or tothe liquid containing capillary material such that heat produced by aheating element may vaporize the liquid. Preferably, filamentarrangement and aerosol-forming substrate are arranged such that liquidmay flow into interstices of the filament arrangement by capillaryaction. The filament arrangement may also be in physical contact with acapillary material.

Preferably, a fluid permeable heating element is a substantially flatheating element. Such a heating element may for example be a flat coilembedded in a porous ceramic or a mesh heater, wherein a mesh or anotherfilament arrangement is arranged over an opening in the heater. Theheating element may for example comprise an electrically conductive meshor coil pattern printed onto a heat resistance support piece. Thesupport piece may for example be ceramic, polyether ether ketone (PEEK),or other thermally resistant ceramics and polymers that do not thermallydecompose and release volatile elements at temperatures below 200 C andpreferably at temperatures below 150 C.

The term ‘filament’ is used throughout the specification to refer to anelectrical path arranged between two electrical contacts. A filament mayarbitrarily branch off and diverge into several paths or filaments,respectively, or may converge from several electrical paths into onepath. A filament may have a round, square, flat or any other form ofcross-section. A filament may be arranged in a straight or curvedmanner.

The term ‘filament arrangement’ is used throughout the specification torefer to an arrangement of one or preferably a plurality of filaments.The filament arrangement may be an array of filaments, for examplearranged parallel to each other. Preferably, the filaments may form amesh. The mesh may be woven or non-woven. Preferably, the filamentarrangement has a thickness of between about 0.5 micrometers and 500micrometers. The filament arrangement may, for example, be in the formof an array of parallel or crosswise electrically conductive filaments.The filament may be integrally formed with electrical contacts, forexample formed from an electrically conductive foil, for example,stainless steel foil, that is etched to define the filaments.

The heating element vaporizes liquid from a cartridge or cartridgehousing comprising an aerosol-forming substrate. The aerosol-formingsubstrate is a substrate capable of releasing volatile compounds thatcan form an aerosol. The volatile compounds may be released by heatingthe aerosol-forming substrate.

The aerosol-forming substrate may comprise plant-based material. Theaerosol-forming substrate may comprise tobacco. The aerosol-formingsubstrate may comprise a tobacco-containing material containing volatiletobacco flavour compounds, which are released from the aerosol-formingsubstrate upon heating. The aerosol-forming substrate may alternativelycomprise a non-tobacco-containing material. The aerosol-formingsubstrate may comprise homogenised plant-based material. Theaerosol-forming substrate may comprise homogenised tobacco material. Theaerosol-forming substrate may comprise at least one aerosol-former. Anaerosol-former is any suitable known compound or mixture of compoundsthat, in use, facilitates formation of a dense and stable aerosol andthat is substantially resistant to thermal degradation at the operatingtemperature of operation of the system. Suitable aerosol-formers arewell known in the art and include, but are not limited to: polyhydricalcohols, such as triethylene glycol, 1,3-butanediol and glycerine;esters of polyhydric alcohols, such as glycerol mono-, di- ortriacetate; and aliphatic esters of mono-, di- or polycarboxylic acids,such as dimethyl dodecanedioate and dimethyl tetradecanedioate.Preferred aerosol formers are polyhydric alcohols or mixtures thereof,such as triethylene glycol, 1,3-butanediol and, most preferred,glycerine. The aerosol-forming substrate may comprise other additivesand ingredients, such as flavourants.

The aerosol forming substrate may be conveyed to the heating element viaa capillary material in contact with or adjacent to the heating element.The capillary material may have a fibrous or spongy structure. Thecapillary material preferably comprises a bundle of capillaries. Forexample, the capillary material may comprise a plurality of fibres orthreads or other fine bore tubes. The fibres or threads may be generallyaligned to convey liquid to the heating element. Alternatively, thecapillary material may comprise sponge-like or foam-like material. Thestructure of the capillary material forms a plurality of small bores ortubes, through which the liquid can be transported by capillary action.The capillary material may comprise any suitable material or combinationof materials. Examples of suitable materials are a sponge or foammaterial, ceramic- or graphite-based materials in the form of fibres orsintered powders, foamed metal or plastics material, a fibrous material,for example made of spun or extruded fibres, such as cellulose acetate,polyester, or bonded polyolefin, polyethylene, terylene or polypropylenefibres, nylon fibres or ceramic. The capillary material may have anysuitable capillarity and porosity so as to be used with different liquidphysical properties. The liquid has physical properties, including butnot limited to viscosity, surface tension, density, thermalconductivity, boiling point and vapour pressure, which allow the liquidto be transported through the capillary device by capillary action.

The capillary material may be in contact with electrically conductivefilaments of the heating element. The capillary material may extend intointerstices between the filaments. The heating element may draw liquidaerosol-forming substrate into the interstices by capillary action. Thecapillary material may be in contact with the electrically conductivefilaments over substantially the entire extent of an aperture in theheating element.

The heating element may be provided in a heating assembly includingsupport elements. The heating assembly may contain two or more differentcapillary materials, wherein a first capillary material, in contact withthe heating element, has a higher thermal decomposition temperature anda second capillary material, in contact with the first capillarymaterial but not in contact with the heating element has a lower thermaldecomposition temperature. The first capillary material effectively actsas a spacer separating the heating element from the second capillarymaterial so that the second capillary material is not exposed totemperatures above its thermal decomposition temperature. As usedherein, ‘thermal decomposition temperature’ means the temperature atwhich a material begins to decompose and lose mass by generation ofgaseous by products. The second capillary material may advantageouslyoccupy a greater volume than the first capillary material and may holdmore aerosol-forming substrate that the first capillary material. Thesecond capillary material may have superior wicking performance to thefirst capillary material. The second capillary material may be a lessexpensive or have a higher filling capability than the first capillarymaterial. The second capillary material may be polypropylene.

According to an aspect of the split airflow system according to theinvention, the first channel converges with an end portion of the secondchannel such that the first flow route joins the second flow route afterthe second flow route has directed ambient air past the heating element,that is the first flow route joins the second flow route downstream ofthe heating element.

In such embodiments ambient air may leave the downstream end of thesplit airflow system or for example a mouthpiece of a smoking system atone or several common outlet openings. Preferably, a most downstreamportion of the second channel is identical with the first channel. Thismay simplify a manufacturing of a smoking system. For example, in amouthpiece a single additional bore may be provided in the mouthpiecewall to extend into the mouthpiece to the second channel to form thefirst channel. By this, also existing mouthpieces may be adapted to asplit airflow system without having to reconstruct the entiremouthpiece. The aerosol containing ambient air is mixed with ‘fresh’ambient air guided into the system by the first flow route. Thereby, theaerosol containing ambient air is cooled. The cool air supports theformation of smaller aerosol droplet sizes compared to the same air at,higher temperatures. Cool air seems to support supersaturation of theair with vaporized liquid. Supersaturation has an effect on the sizes ofdroplets formed in the supersaturated air.

According to an alternative aspect of the split airflow system accordingto the invention, the first channel and the second channel form distinctchannels such that the first flow route and the second flow route directambient air from outside the system to the downstream end of the systemseparate from each other. Thus, ambient air is drawn into the splitairflow system, guided in and though the system and out of the systemalong entirely separate flow routes. By this, ambient air passing theheating element and ambient air bypassing the heating element do notcompete or influence each other. Having a separate first channelprovides many constructional possibilities to guide ambient air thoughthe system or through a mouthpiece independent of the aerosol carryingambient air in the second channel.

According to another aspect of the split airflow system according to theinvention, at least a portion of the second channel and the heatingelement are arranged perpendicular to each other such that the at leasta portion of the second channel directs ambient air to impingeperpendicular onto the heating element.

Letting ambient air to impinge onto the heating element is an efficientway to direct ambient air to the heating element and carry aerosol awayfrom the heating element. In particular, if the ambient air impingesonto the center of a heating element, a homogeneous airflow over theheating element may be provided in a radially outward direction. Theambient air may impinge onto the center only of the heating element.

In the split airflow system according to the invention, at least aportion of the second channel arranged downstream of the heatingelement, may be arranged in the circumference of the heating element,preferably in the circumference only.

Preferably, a plurality of second channel portions is arranged in thecircumference of the heating element. By this the vapour containingambient air is guided away from the heating element at the circumferenceof the heating element, for example in longitudinal direction along thecircumference of, for example, a housing or a mouthpiece of anelectrically heated smoking system. The large area such vapourcontaining ambient air is guided along, as well as the closeness to anenvironment may both support a cooling of the vapour containing air andsupport aerosol formation. If at least a channel portion of a firstchannel is arranged parallel to the at least one portion of thecircumferentially arranged second channel arranged downstream of theheating element, additional cooling may be provided through freshambient air flowing through the first channel portion and thermalcontact between the respective first channel portions and second channelportions. Preferably, a plurality of first channel portions is arrangedin longitudinal direction along the circumference of a mouthpiece. Anarrangement of channel portions in a circumference only, leaves optionsof having other channels arranged in, for example, of a center only orhaving radially arranged channel portions connecting central andcircumferential channel portions or central channel portions with theenvironment.

The first flow route and the second flow route may be selected toachieve a desired result, for example a predefined airflow splittingwith predefined air volumes passing through the respective channels. Forexample, a length or diameter of a channel may be varied, for examplealso to achieve a predefined resistance to draw (RTD). First and secondflow route are also selected according to a set-up of an aerosolgenerating smoking system and the arrangement and characteristics of theindividual components of the smoking system. For example, aerosol may begenerated at a proximal end or at a distal end of a cartridge housingcontaining the aerosol-forming substrate. Depending on the orientationof the cartridge in the aerosol-generating smoking system, the open endof the cartridge housing is arranged to face a mouthpiece or is arrangedfacing away from the mouthpiece. Accordingly, a heating element forheating the aerosol-forming substrate is arranged at a proximal ordistal end of the housing. Preferably, liquid is vaporized at the opendistal end of the mouthpiece and a heating element is arranged betweencartridge and mouthpiece.

Preferably, a first flow route and first channel, accordingly, areentirely arranged in a mouthpiece of the smoking system. Preferably, afirst air inlet is then arranged in a side wall of the mouthpiece, whilethe one or several outlets of the first channel are arranged in theproximal or mouth end of the mouthpiece. A second flow route isdependent on the location of the heating element in the smoking system.For example, if a heating element is arranged at an open proximal end ofthe cartridge housing, for example to cover the proximal end of thecartridge (top version), the second channel may also be arrangedentirely in a mouthpiece.

The first channel and the second channel may diverge into severalchannel portions and several channel portions of a first channel or of asecond channel may converge into a single first channel or secondchannel, respectively. In addition, a first channel may consist ofseveral first partial channels and a second channel may consist ofseveral second partial channels. There, a sum of first partial channelsprovide for the volume of ambient air of the first channel and a sum ofsecond partial channels provide for the volume of ambient air of thesecond channel. The total number of air inlets for both the first andsecond partial channels may preferably be between 2-10, more preferablybetween 6-10, and most preferably between 8-10. For example, a sum offirst partial channels that provide for the volume of ambient air of thefirst channel may have 7 or 9 inlets in fluid communication with thefirst channel and a sum of second partial channels provide for thevolume of ambient air of the second channel via 1 or 2 inlets in fluidcommunication with the second channel.

In embodiments where a heating element is arranged at an open distal endof a cartridge housing, for example to cover the open distal end of thecartridge (bottom version), the second flow route routinely starts at afurther distal location in the smoking system, for example in the regionof a distal end of the cartridge housing. A second air inlet of thesecond channel may for example be arranged in a main housing of thesystem. Ambient air is then directed into the system, passes the heatingelement at the distal end of the cartridge and entrains vapour generatedby heating the aerosol-forming substrate in the cartridge. The aerosolcontaining air may then be guided along the cartridge between acartridge housing and a main housing to the downstream end of thesystem, where it is mixed with ambient air from the first flow route(either before or upon reaching the downstream end).

An inlet opening of the second channel arranged in a region of a distalend of a cartridge housing may also be provided in a top version, thatis in embodiments, where a heating element is arranged at a proximal endof the cartridge. The second flow route may not only pass outside of thecartridge but also through the cartridge. Ambient air then enters thecartridge at a semi-open wall of the cartridge, passes through thecartridge and leaves the cartridge by passing though the heating elementarranged at the proximal end of the cartridge. Thereby, ambient air maypass through the aerosol-forming substrate or through one or severalchannels arranged in a solid aerosol-forming substrate such that ambientair does not pass through the substrate itself but in the channels nextto the substrate.

For allowing ambient air to enter a cartridge, a side wall of thecartridge housing, preferably a wall opposite the heating element,preferably a bottom wall, is provided with at least one semi-open inlet.The semi-open inlet allows air to enter the cartridge but no air orliquid to leave the cartridge through the semi-open inlet.

A semi-open inlet may for example be a semi-permeable membrane,permeable in one direction only for air but is air- and liquid-tight inthe opposite direction. A semi-open inlet may for example also be aone-way valve. Preferably the semi-open inlets allow air to pass throughthe inlet only if specific conditions are met, for example a minimumdepression in the cartridge or a volume of air passing through the valveor membrane.

Such one-way valves may, for example, be commercially available valves,such as for example used in medical devices, for example LMS MediflowOne-Way, LMS SureFlow One-Way or LMS Check Valves (crosses membranes).Suitable membranes to be used for a cartridge having an airflow passingthrough the cartridge, are for example vented membranes as used inmedical devices, for example Qosina Ref. 11066, vented cap withhydrophobic filter or valves as used in baby bottles.

Such valves and membranes may be made of any material suitable forapplications in electrically heated smoking systems. Materials suitablefor medical devices and FDA approved materials may be used; for exampleGraphene having very high mechanical resistance and thermal stabilitywithin a large range of temperatures. Preferably, valves are made ofsoft resilient material for supporting a liquid-tight incorporation ofthe one or several valves into a wall of the cartridge housing.

Letting ambient air pass through the substrate supports anaerosolization of the aerosol-forming substrate. During puffing, adepression occurs in the cartridge, which may activate the semi-openinlets. Ambient air then passes the cartridge, preferably a highretention or high release material (HRM) or a liquid, and crosses theheating element, thereby creating and sustaining aerosolization of theliquid, when the heating element sufficiently heats the liquid. Inaddition, due to the depression caused during puffing, a supply ofliquid in a transport material such as a capillary material to theheating element may be limited. An ambient airflow through the cartridgemay equalize pressure differences within the cartridge and therebysupport an unhindered capillary action towards the heating element.

A semi-open inlet may, in addition, or alternatively also be provided inone or several side walls of the cartridge housing. Semi-open inlets inside walls provide a lateral airflow into the cartridge towards the opentop end of the cartridge housing, where the heating element is arranged.Preferably, lateral airflows pass through the aerosol-forming substrate.

If an air inlet of a second channel is arranged in a mouthpiece, a wayfrom the inlet to the heating element may be kept short thus possiblyreducing a resistance to draw. Air may also be guided in radialdirection from one side of the heating element to the other side or, forexample, from a peripheral side of the heating element to the center ofthe heating element.

The second flow route may provide many variants to supply ambient air tothe heating element and transport aerosol away from the heating elementand to a downstream end of the system. For example, a radial supply ofambient air is preferably combined with and large central extraction. Acentral supply of ambient air is preferably combined with a radialdistribution of the air over an entire heating element surface with acircumferential conveying of the aerosol containing air to thedownstream end. The second flow route may direct ambient air to impingeonto the heating element, for example perpendicular to the heatingelement, preferably onto a center of the heating element.

Airflow directed perpendicularly or parallel to a center portion ofheating element demonstrates improved aerosolization in terms of smallerparticle sizes and higher amounts of total particulate matter present inthe aerosol stream when compared to airflow that impinges the surface atan angle greater than 0 and less than 90 degrees. This may be due to alower level of turbulences created at the heater element and airflowinterface, improved aerosol production by maximizing the whole of theheater (for example, portions outside of the center port ion of theheater element contribute additional or higher amounts of aerosol), ordue to a higher wicking effect based on a higher volume of air crossingthe heating element.

According to another aspect of the invention, there is provided a methodfor guiding an airflow in an electrically heated smoking system forgenerating aerosol. The method comprises the steps of directing ambientair from outside the system to a downstream end of the system along afirst flow route and directing ambient air from outside the systemtowards a heating element, preferably a substantially flat, fluidpermeable heating element, before conveying the ambient air to thedownstream end of the system along a second flow route. Therein, a totalvolume of ambient air passes through the system along the first flowroute and along the second flow route, and at least 50 percent of thetotal volume of ambient air through the system passes along the firstflow route.

According to an aspect of the method according to the invention, themethod further comprises the step of joining ambient air of the firstflow route and ambient air of the second flow route before the ambientair of the first flow route and of the second flow route reach thedownstream end of the system.

According to another aspect of the method according to the invention,the method further comprises the step of keeping the first flow routeseparate from the second flow route.

According to yet another aspect of the method according to theinvention, the method comprises the step of directing the ambient air inthe second flow route such that the ambient air in the second flow routeimpinges substantially perpendicularly onto the heating element.

Further aspects and advantages of the method according to the inventionare mentioned relating to the split airflow system and smoking systemaccording to the invention and will not be repeated.

According to a further aspect of the method according to the invention,the method further comprises the steps of providing a liquid aerosolforming substrate, heating the heating element, thereby vaporizingliquid from the aerosol forming substrate and forming aerosol andletting the ambient air directed to the heating element by the secondflow route pick up the formed aerosol before conveying the aerosolcontaining ambient air to the downstream end of the system.

According to another aspect of the method according to the invention,the method further comprises the steps of providing at least a portionof the first channel and at least a portion of the second channel insidea mouthpiece of the system, wherein the downstream end of the system isa proximal end of the mouthpiece. The method further comprises the stepsof guiding ambient air in the at least a portion of the second channelalong a length of the mouthpiece in a direction towards the proximal endof the mouthpiece, performing an inversion of direction of the ambientair in the second channel, and guiding the ambient air in the directionof the heating element for impinging the ambient air onto the heatingelement.

According to some embodiments of the method according to the invention,the ambient air is guided in the at least a portion of the secondchannel along a central axis of the mouthpiece, and is made to impingesubstantially centrally onto the heating element.

The method may further comprise the steps of guiding aerosol containingambient air from a center of the heating element, where the ambient airpreferably impinged perpendicularly onto the heating element, radiallyoutwardly to the circumference of the heating element andcircumferentially downstream into the direction of an outlet opening.The step of guiding the aerosol containing ambient air circumferentiallydownstream may, for example, be performed in a plurality ofcircumferentially arranged channel portions.

The method may comprise the step of arranging a substantially flat fluidpermeable heating element in the electrically heated smoking system.Preferably, the heating element is arranged in a manner to face an opendistal end of the mouthpiece of the smoking system. Preferably, thefluid permeable heating element comprises a plurality of electricallyconductive filaments. A plurality of filament, for example an array ofparallel arranged filaments or a mesh, provide a good vaporization ofliquid and a good permeability of vaporized liquid through intersticesbetween the filaments. Such filaments or mesh heating elements areinexpensive to produce and robust, especially compared to coil and wickheaters. Mesh heating elements may be manufactured in a substantiallyflat manner, which is space saving. Mesh heating elements are also easyto handle, especially upon mounting of the heating element or cartridgecomprising the heating element.

According to yet another aspect of the invention, there is also providedan electrically heated smoking system for generating aerosol comprisingthe split airflow system as described herein. The smoking systemcomprises a storage portion comprising a housing for holding a liquidaerosol-forming substrate, the housing having an open end. The smokingsystem also comprises a heating element, preferably a substantiallyflat, fluid permeable heating element, extending over the open end ofthe housing and a mouthpiece arranged adjacent the housing. Themouthpiece comprises an elongate body comprising an open distal end, theopen distal end facing the housing. The mouthpiece further comprises afirst channel arranged in the mouthpiece, wherein the first channelcomprises a first inlet opening arranged in a side wall of the elongatebody and an outlet opening arranged at a proximal end of the elongatebody for defining a first flow route directing ambient air from outsidethe system through the mouthpiece to the outlet opening. The mouthpiecealso comprises an end portion of a second channel extending between theopen distal end of the elongate body and the proximal end of theelongate body. The second channel is arranged in the smoking system anddefines a second flow route. The second flow route directs ambient airentering the smoking system to the heating element, where the ambientair is capable of entraining aerosol generated by vaporizing liquidthrough heating the heating element, before conveying the aerosolcontaining ambient air to the proximal end of the elongate body of themouthpiece. The first channel and the second channel define a totalvolume of ambient air passing through the smoking system and the firstchannel provides at least 50 percent of the total volume of ambient airpassing through the smoking system. Ambient air from outside the systemis split to pass along a first flow route in the first channel and topass along a second route in the second channel.

Preferably, the heating element is arranged between the mouthpiece andthe aerosol generating substrate.

According to an aspect of the smoking system according to the invention,the first channel converges with the end portion of the second channeldownstream of the open distal end of the elongate body. By this, theambient air of the first channel does not pass the heating element. Afirst inlet opening of the first channel is fluidly connected to anoutlet opening at the downstream end of the system, that is, in theproximal end of the mouthpiece.

According to another aspect of the smoking system according to theinvention, the second channel comprises a second outlet opening arrangedat the proximal end of the elongate body. The second outlet opening isseparate from the outlet opening of the first channel.

According to a further aspect of the smoking system according to theinvention, a second inlet opening of the second channel is arranged inthe side wall of the elongate body.

In the smoking system according to the invention, the second channel maycomprise at least one second channel portion arranged downstream of theheating element carrying the aerosol containing ambient air. The atleast one second channel portion is arranged in longitudinal directionalong the circumference of the housing or of the mouthpiece.

Aspects and advantages of the electrically heated smoking system havebeen described relating to the split airflow system and method forguiding an airflow in an electrically heated smoking system and will notbe repeated.

According to some embodiments of the smoking system according to theinvention an upstream portion of the second channel is arranged parallelto a side wall of the elongate body of the mouthpiece or of the housingbefore an intermediate portion of the second channel directs in a radialdirection of the elongate body. Such a flow route may for example beused to direct the ambient air to be guided essentially parallel toportions of the ambient air already carrying aerosol. By this, anadditional cooling of the aerosol by the ambient air may be achieved.

According to another aspect of the smoking system according to theinvention, the heating element is a fluid permeable heating elementcomprising a plurality of electrically conductive filaments.

According to a further aspect of the smoking system according to theinvention, the second channel comprises a plurality of second channelend portions arranged in longitudinal direction along the circumferenceof the elongate body. Preferably, ambient air is guided to the center ofthe heating element. A homogeneous extraction of aerosol from theheating element with the ambient air may be provided: the centrallyimpinging ambient air may flow radially outwardly on the surface of theheating element. In addition, the aerosol containing ambient air may becooled on a large total surface area, which may further supportformation of small-sized aerosol particles.

The invention is further described with regard to embodiments, which areillustrated by means of the following drawings, wherein:

FIG. 1 shows an embodiment of the split airflow system;

FIG. 2 shows another embodiment of a second flow route in the splitairflow system;

FIG. 3 shows the cooling effect of different airflows on differentheating element;

FIG. 4 shows temperature curves of differently powered heating elements;

FIG. 5 shows temperature curves at the outlet of the mouthpiece;

FIG. 6 shows average vapour saturation curves at the outlet of themouthpiece;

FIG. 7 shows the ratio of droplet diameters at the outlet of themouthpiece for total and split airflow geometries;

FIG. 8a to 8f shows heating elements as may be used in the smokingsystem according to the invention;

FIG. 9a,9b are detailed views of the filaments of the heating elements,showing a meniscus of liquid aerosol-forming substrate between thefilaments (FIG. 9a ) and a capillary material extending between thefilaments (FIG. 9b );

FIG. 10 shows a cross-section of a cartridge system with highretention-release material (HRM) and air passage through the HRM;

FIG. 11 shows a cross-section of another cartridge system with highretention-release material (HRM) and air passage through the cartridge;

FIG. 12 shows an exploded view of the cartridge system of FIG. 11;

FIG. 13 shows a cross-section of a cartridge system with a liquid andair passage through the liquid.

In FIG. 1 a cartridge 4 and mouthpiece 1 embodiment for an aerosolgenerating smoking system is shown. An elongate main housing 5accommodates a cartridge with a tubular shaped cartridge housing 4containing an aerosol-forming substrate, for example a liquid containingcapillary material 41. The cartridge housing has an open proximal end42. A heater 30, preferably, a substantially flat mesh heater, isarranged to cover the open proximal end of the cartridge housing 4. Theheating element may or may not be in direct physical contact with theaerosol-forming substrate 41. A mouthpiece 1 having a substantiallytubular shaped elongate body 15 is aligned with the main housing, thecartridge housing 4 and the heating element 30. The elongate body 15 hasan open distal end facing the heater 30.

The embodiment shown in FIG. 1 comprises a second channel 10 defining asecond flow route in the mouthpiece 1 leading incoming second ambientair 20 over the heater 30 and to air outlets 12 at a proximal end ormouth end of the mouthpiece 1, where a consumer puffs. Also a firstchannel 11 defining a first flow route is arranged in the mouthpiece 1.First ambient air 21 enters the first channel 11 through a first inlet110 and is directly led to the outlets 12 without passing the heater 30.This first airflow 21 joins the second airflow 20 in the second channel10 at a location 111 downstream of the heater 30 and upstream of theoutlets 12. A most downstream portion of the second channel 10 isidentical with the first channel 11. The second airflow 20 passes theheater 30, where aerosol formed by heating the heater and vaporizingliquid from the aerosol-forming substrate 41, and entrains the aerosolin the second airflow 21. The aerosol carrying second airflow iscombined with the first airflow 21 at location 111. The first airflow 21mixes with the aerosol carrying second airflow and cools it.

Second inlet 100 and first inlet 110 are both openings or bore holes inthe mouthpiece 1 in a distal half of the elongate body 15 of themouthpiece 1. The second flow route in an upstream second channelportion 101 runs in the elongate body parallel to the circumference ofthe elongate body to the proximal end of the mouthpiece. In a radiallyinwardly directing portion 102 of the second channel 10, the secondairflow 20 is directed to the center of the elongate body and in acentrally arranged portion 103 of the second channel the second airflow20 is directed to the heater 30 to impinge to the center 31 of theheater 30. The second airflow 20 passes over the heater 30 and spreadsradially outwardly to several longitudinal end portions 104 of thesecond channel 10. The longitudinal end portions 104 are regularlyarranged along the circumference within the elongate body.

In this embodiment a first flow route and a second flow route and afirst channel and a second channel, respectively, are arranged entirelywithin the mouthpiece 1 of the aerosol generating system.

In FIG. 2 an embodiment of a cartridge 4 with heater 30 arranged at thebottom of the cartridge covering an open distal end 43 of the cartridgehousing 41 is illustrated. A second inlet 100 is arranged in the mainhousing 5 and the ambient air is directly led in a radially inwardlydirecting portion 102 of the second channel to the center of the mainhousing. In a centrally arranged portion 103 of the second channel, theair is directed to impinge perpendicularly onto the heater 30. The airthen passes the heater 30, entrains aerosol caused by heating the liquidin the aerosol-forming substrate 40 through the heater 30. The aerosolcontaining air is led to the proximal end of the cartridge 4 in severallongitudinal portions 105 of the second channel 10 arranged between andalong cartridge housing 41 and main housing 5. There, the aerosolcontaining second airflow is guided to and out of a single centrallyarranged opening 52 in the main housing 5. A mouthpiece (not shown) maybe arranged adjacent the main housing. Preferably, the mouthpiece thenalso has a centrally arranged opening and end portion 104 of secondchannel 10 to receive the aerosol containing second airflow and guide itto a single outlet opening 12 in the proximal end of the mouthpiece 1.In such an embodiment, a first channel 11 may basically be similar tothe embodiment shown in FIG. 1. The first channel may be a separatechannel in the mouthpiece or may comprise a radial bore that extends tothe second channel in the mouthpiece such that the first airflow 21 maybe joined with the second airflow within the mouthpiece.

The data shown in rig. 3 demonstrate the effect of cooling a mesh heaterthe more the higher a flow rate of air passing the mesh heater. Coolingrates were measured using different mesh heaters: Peking (45micrometers/180 per inch), Haver (25 micrometers/200 per inch) and 3strips Warrington (25 micrometers/250 per inch). Measurement data forthe Reking heater are indicated by crosses, measurement data for theHaver heater are indicated by circles and measurement data for the 3strips Warrington heater are indicated by triangles. All heaters wereoperated at three Watt. Temperature was measured with a thermocouplecoupled to the heaters. Increasing the flow rate as indicated on thex-axis in liter per minute [L/min] results in a lower measuredtemperature on the mesh heater. Typical sizes of airflows inaerosol-generating systems can be approximated by standard smokingregimes, for example the Health Canada smoking regime, which leads tosignificant cooling of the heater. Exemplary smoking regimes such asHealth Canada draw 55 ml of a mix of air and vapour over 2 seconds. Analternative regime is 55 ml over 3 seconds. Neither exemplary smokingregime mimics behaviour precisely but instead acts as a proxy to what anaverage user would draw.

Experiments with split airflow systems were preferably made with thefirst airflow having between 6/7 and 8/9 of the total volume of ambientair. The volume of ambient air directed to the heater had a volumebetween 1/7 and 1/9 of the total volume of ambient air, accordingly.About 85 percent to 89 percent of the total volume of ambient air isthus directly conveyed through the outlet of the mouthpiece, while onlyabout 11 percent to about 15 percent of the total volume of airflow passthe heater.

Exemplary values for the channels as for example shown in the embodimentof FIG. 1, are:

Air inlet of the second channel: diameter 0.75 millimeter and totalchannel cross section 0.44 square millimeter.

Air inlet of first channel: diameter 1 millimeter times 4 and 3.14square millimeter total channel cross section.

In the graph of FIG. 4, average temperatures at the heater versus timeduring one puff is shown. Curve 60 represents reference temperature datafor the heater, where the total airflow is directed to the heater. Curve70 represents temperature data for the heater in a split airflow system,where only one/seventh of the total airflow is directed to the heater.For the reference data the heater had been heated with 5 Watt, while theheater receiving a reduced airflow had been heated with 4 Watt. It canbe seen that with a split airflow, energy of 1 Watt during the length ofone puff may be saved.

FIG. 5 shows the effect of the split airflow onto the temperature of theaerosol carrying airflow at the outlet of the mouthpiece during onepuff. These data refer to embodiments of mouthpieces, where the firstairflow joins the aerosol carrying second airflow within the mouthpiece,as shown in FIG. 1. Temperature curve 61 represents outlet airtemperatures for a heater powered with 5 Watt with the total airflowimpinging on the heater. Temperature curve 71 represents outlet airtemperatures for a heater powered with 4 Watt, where one/seventh of thetotal airflow only is directed to the heater. There are significantlower temperatures of the aerosol carrying airflow at the outlet of themouthpiece due to the six/seventh volume of ‘fresh’ air joining theaerosol stream. Typically ‘fresh’ air mixed into the aerosol carryingairflow is at room temperature.

Significant difference may also be seen in the ratio of vapour pressureto the saturation pressure (Pvapor/Psaturation) of a glycerol solutionat the outlet of the mouthpiece during one puff. This ratio is shown inFIG. 6. Curve 72 refers to pressure data at the outlet for the heaterpowered with 4 Watt, in the split airflow system with one/seventh of thetotal airflow directed to the heater. Curve 62 refers to pressure dataat the outlet for the heater powered with 5 Watt with the total airflowimpinging on the heater. The pressure ratio is higher for the splitairflow embodiment due to the cooling effect. This represents a largerdegree of super saturation of the glycerol solution, which favoursaerosolization with smaller droplets. Simulation clearly predictssmaller droplet sizes for the cooler vapour of the split airflowembodiment compared to vapour of non-split or total airflow embodiments.These simulation data 67 are shown in FIG. 7 for one puff at the outletof the mouthpiece. Y-Axis represents the ratio of droplet diameters forsplit airflow to total airflow systems.

The ratios are calculated and shown as d_split/d_ref=T*Ln (S) ref/T*Ln(S) split versus time (in seconds) during one puff on theaerosol-generating system where T is the temperature expressed indegrees Kelvin and S is the saturation ratio which is a function of Pvand (T).

FIG. 8a is an illustration of a first heating element 30. The heatingelement comprises a mesh 36 formed from 304L stainless steel, with amesh size of about 400 Mesh US (about 400 filaments per inch). Thefilaments have a diameter of around 16 micrometer. The mesh is connectedto electrical contacts 32 that are separated from each other by a gap 33and are formed from a copper foil having a thickness of around 30micrometer. The electrical contacts 32 are provided on a polyimidesubstrate 34 having a thickness of about 120 micrometer. The filamentsforming the mesh define interstices between the filaments. Theinterstices in this example have a width of around 37 micrometer,although larger or smaller interstices may be used. Using a mesh ofthese approximate dimensions allows a meniscus of aerosol-formingsubstrate to be formed in the interstices, and for the mesh of theheating element to draw aerosol-forming substrate by capillary action.The open area of the mesh, that is, the ratio of the area of intersticesto the total area of the mesh is advantageously between 25 percent and56 percent. The total resistance of the heating element is around 1 Ohm.The mesh provides the vast majority of this resistance so that themajority of the heat is produced by the mesh. In this example the meshhas an electrical resistance more than 100 times higher than theelectrical contacts 32.

The substrate 34 is electrically insulating and, in this example, isformed from a polyimide sheet having a thickness of about 120micrometer. The substrate is circular and has a diameter of 8millimeter. The mesh is rectangular and has side lengths of 5 millimeterand 2 millimeter. These dimensions allow for a complete system having asize and shape similar to a convention cigarette or cigar to be made.Another example of dimensions that have been found to be effective is acircular substrate of diameter 5 millimeter and a rectangular mesh of 1millimeter times 4 millimeter.

FIG. 8b and FIG. 8c are illustrations of other alternative heatingelements. In the heating element of FIG. 8b the filaments 37 are bondeddirectly to substrate 34 and the contacts 32 are then bonded onto thefilaments. The contacts 32 are separated from each other by insulatinggap 33 as before, and are formed from copper foil of a thickness ofaround 30 micrometer. The same arrangement of substrate filaments andcontacts can be used for a mesh type heater as shown in FIG. 8a . Havingthe contacts as an outermost layer can be beneficial for providingreliable electrical contact with a power supply.

The heating element of FIG. 8c comprises a plurality of heater filaments38 that are integrally formed with electrical contacts 39. Both thefilaments and the electrical contacts are formed from a stainless steelfoil that is etched to define filaments 38. The contacts 39 areseparated by a gap 33 except when joined by filaments 38. The stainlesssteel foil is provided on a polyimide substrate 34. Again the filaments38 provide the vast majority of the resistance, so that the majority ofthe heat is produced by the filaments. In this example the filaments 38have an electrical resistance more than 100 times higher than theelectrical contacts 39.

FIGS. 8d to 8e show several heating elements having a mesh 36 fixed toand between two contact portions 35. The mesh is fixed on both sides tothe contact portions 35. Each contact portion has a round outercircumference and two openings 351. The heating elements 30 may beattached to the housing of a cartridge or to a supporting substrate bytheses openings 351, for example by screwing.

Capillary material 41 is advantageously oriented in the housing 4 toconvey liquid to the heating element 30. When the cartridge isassembled, the heater filaments 36, 37, 38 may be in contact with thecapillary material 41 and the aerosol-forming substrate can be conveyeddirectly to the mesh heater. FIG. 9a is a detailed view of the filaments36 of the heating element, showing a meniscus 46 of liquidaerosol-forming substrate between the heater filaments 36. It can beseen that aerosol-forming substrate contacts most of the surface of eachfilament so that most of the heat generated by the heating elementpasses directly into the aerosol-forming substrate.

FIG. 9b is a detailed view, similar to FIG. 9a , showing an example of acapillary material 41 that extends into the interstices between thefilaments 36. The capillary material 41 may be a capillary materialarranged next to the or in contact with the heating element, preferablyhaving a high temperature resistance. It can be seen that by providing acapillary material comprising fine threads of fibres that extend intothe interstices between the filaments 36, transport of liquid to thefilaments can be ensured.

In use the heating elements operate by resistive heating. Current ispassed through the filaments 36,37,38, under the control of controlelectronics (not shown), to heat the filaments to within a desiredtemperature range. The mesh or array of filaments has a significantlyhigher electrical resistance than the electrical contacts 32,35 andelectrical connectors (not shown) so that the high temperatures arelocalised to the filaments. The system may be configured to generateheat by providing electrical current to the heating element in responseto a user puff or may be configured to generate heat continuously whilethe device is in an “on” state.

Different materials for the filaments may be suitable for differentsystems. For example, in a continuously heated system, graphitefilaments are suitable as they have a relatively low specific heatcapacity and are compatible with low current heating. In a puff actuatedsystem, in which heat is generated in short bursts using high currentpulses, stainless steel filaments, having a high specific heat capacitymay be more suitable.

In rig. 10 a cross section of a cartridge system, wherein a second flowroute comprises an airflow directed through the cartridge isillustrated. A fluid permeable heater, for example a mesh heater 30, isprovided to cover the open top of the housing 4. For sealing the top ofthe housing 4, a sealing layer 48, for example a polymer layer, isprovided between the upper rim of the housing 4 and the heater 30. Inaddition, a sealing disc 47, for example a polymer disc, is provided onthe top side of the heater 30. With the sealing disc 47 airflow throughthe heater may be controlled, in particular, airflow constraints may beprovided. The sealing disc may also be arranged on the bottom side ofthe heater 30.

The cartridge housing 4 comprises a liquid containing high retentionmaterial or high release material (HRM) 41 serving as liquid reservoirand directing liquid towards the heater 30 for evaporation at theheater. A capillary disc 44, for example a fiber disc, is arrangedbetween HRM 41 and heater 30. The material of the capillary disc 44 maybe more heat resistant than the HRM 41 due to its closeness to theheater 30. The capillary disc is kept wet with the aerosol-formingliquid of the HRM to secure provision of liquid for vaporization if theheater is activated.

The housing 4 is provided with an air permeable bottom 45. The airpermeable bottom is provided with an airflow inlet 450. The airflowinlet 450 allows air to flow through the bottom 45 into the housing inone and this direction only. No air or liquid may leave the housingthrough the air permeable bottom 45. The air permeable bottom 45 may forexample comprise a semi-permeable membrane as airflow inlet 450 or maybe a bottom cover comprising one or more one-way valves as will be shownbelow.

If low depression prevails on the side of the heater, as is the caseduring puffing, air may pass through the airflow inlet 450 into thecartridge. The airflow 20 will pass through the HRM 41 and through theheater 30. The aerosol containing airflow 20 will then flow to adownstream end of the aerosol generating device, preferably in acentrally arranged channel in a mouthpiece.

Side walls of the housing 4 may also be provided with lateral airpermeable sections 46 for providing lateral airflows into the housing.Lateral air permeable sections 46 may be designed as the airflow inlets450 in the air permeable bottom 45.

In FIG. 11 the arrangement and function of the cartridge system isbasically the same as shown in FIG. 10. However, the HRM 41 is providedwith a central opening 412. Air entering the airflow inlet 450 in thebottom 45 of the housing passes through the central opening 412. Theairflow passes next to the HRM in the cartridge. With optional lateralair permeable sections 46 in the side wall of the housing 4, lateralairflow may be provided through the HRM 41.

In FIG. 12 an exploded view of cartridge system as in FIG. 11 is shown.A ring-shaped tubular HRM 41 is provided in the housing 4. The bottom 45of the housing is a disc comprising a one-way valve 49 arranged in thecenter of the disc and aligned with the central opening 412 in the HRM41. Such a one-way valve may for example be a commercially availablevalve, such as for example used in medical devices or in baby bottles.

FIG. 13 is a cross section of another embodiment of a cartridge system.Same reference numerals are used for the same or similar elements. Inthis embodiment, the housing 4 is filled with an aerosol-forming liquid411. The housing may be made of metal, plastics material, for example apolymeric material, or glass. The valve 49 may directly be molded intothe bottom 45 of the housing. The bottom 45 may also be provided with acavity for air-tight assembly with the valve. Due to the valvespreferably being made of a flexible material, tight assembly with thebottom material may be achieved.

In the above cartridge systems as described in FIG. 10 to FIG. 13 thecartridge housing 4 may also be a separate cartridge container inaddition to the cartridge housing as described for example in FIG. 1.Especially, a liquid 411 containing cartridge is a pre-manufacturedproduct, which may be inserted into a cartridge housing provided in theaerosol generating system for receiving the pre-manufactured cartridge.

1.-38. (canceled)
 39. An assembly for an aerosol-generating system, theassembly comprising: a liquid storage portion configured to hold aliquid aerosol-forming substrate; a mouthpiece having an outlet openingat a proximal end thereof; and a heater assembly comprising: anelectrical heating element configured to heat the liquid aerosol-formingsubstrate to form an aerosol, and a porous capillary material disposedin contact with the electrical heating element and comprising a ceramicor a ceramic-based material, the electrical heating element beingdisposed along a surface of the porous capillary material, wherein theliquid storage portion is disposed at a first side of the heaterassembly and a first airflow channel is disposed at a second side of theheater assembly, the first airflow channel defining an airflow path thatextends in a direction perpendicular to the surface of the porouscapillary material and is directed at a center of the electrical heatingelement.
 40. The assembly according to claim 39, wherein a secondairflow channel extends from the heater assembly from one side of theliquid storage portion to the outlet opening of the mouthpiece.
 41. Theassembly according to claim 39, wherein the electrical heating elementcomprises a filament disposed in a curved manner between two electricalcontacts respectively connected to ends of the filament.
 42. Theassembly according to claim 41, wherein the filament is substantiallyflat.
 43. The assembly according to claim 39, wherein the heaterassembly further comprises two electrical contacts.
 44. The assemblyaccording to claim 43, wherein the heater assembly further comprises anelectrically insulating support having an opening.
 45. The assemblyaccording to claim 44, wherein the two electrical contacts are supportedby the electrically insulating support.
 46. The assembly according toclaim 39, wherein the electrical heating element is embedded in theporous capillary material.
 47. The assembly according to claim 39,wherein the electrical heating element is printed onto the surface ofthe porous capillary material.
 48. The assembly according to claim 39,wherein the capillary material is selected from a group consisting of aceramic-based material of sintered powder, a fibrous material, and acombination.
 49. The assembly according to claim 39, wherein thecapillary material is in fluid connection with the liquidaerosol-forming substrate.
 50. An aerosol-generating system comprisingan assembly, the assembly comprising: a liquid storage portionconfigured to hold a liquid aerosol-forming substrate; a mouthpiecehaving an outlet opening at a proximal end thereof; and a heaterassembly comprising: an electrical heating element configured to heatthe liquid aerosol-forming substrate to form an aerosol, and a porouscapillary material disposed in contact with the electrical heatingelement and comprising a ceramic or a ceramic-based material, theelectrical heating element being disposed along a surface of the porouscapillary material, wherein the liquid storage portion is disposed at afirst side of the heater assembly and a first airflow channel isdisposed at a second side of the heater assembly, the first airflowchannel defining an airflow path that extends in a directionperpendicular to the surface of the porous capillary material and isdirected at a center of the electrical heating element.
 51. A heaterassembly for an aerosol-generating system, the heater assemblycomprising: an electrically insulating support having an opening; anelectrical heating element disposed across the opening in theelectrically insulating support and being configured to heat a liquidaerosol-forming substrate to form an aerosol, the electrical heatingelement being substantially flat and planar; a porous capillary materialdisposed in contact with the electrical heating element, the porouscapillary material comprising a ceramic or a ceramic-based material andbeing configured to convey the liquid aerosol-forming substrate to theelectrical heating element, the electrical heating element being furtherdisposed along a surface of the porous capillary material; and twoelectrical contacts respectively connected to ends of the electricalheating element, the two electrical contacts being supported by theelectrically insulating support.
 52. The heater assembly according toclaim 51, further comprising a first airflow channel disposed at oneside of the heater assembly, the first airflow channel defining anairflow path that extends in a direction perpendicular to the surface ofthe porous capillary material, and is directed at a center of theelectrical heating element.
 53. The heater assembly according to claim51, wherein the electrical heating element comprises a filament disposedin a curved manner between the two electrical contacts.
 54. The heaterassembly according to claim 53, wherein the filament is substantiallyflat.
 55. The heater assembly according to claim 51, wherein theelectrical heating element is embedded in the porous capillary material.56. The heater assembly according to claim 51, wherein the electricalheating element is printed onto the surface of the porous capillarymaterial.
 57. The heater assembly according to claim 51, wherein thecapillary material is selected from a group consisting of aceramic-based material of sintered powder, a fibrous material, and acombination.
 58. The heater assembly according to claim 51, wherein thecapillary material is in fluid connection with the liquidaerosol-forming substrate.